Approximately 1% of babies born require operative treatment for congenital heart diseases. Worldwide, 80,000 pediatric cardiac procedures are performed annually. These procedures are all performed postnatally. However, based on a growing recognition that earlier anatomic repair is beneficial to the health of the child, it has become clear that prenatal cardiac intervention (PCI), though revolutionary, is highly desirable to correct aortic valve stenoses and other abnormalities that lead to hypoplastic left heart syndrome (HLHS). At the same time the technology available for PCI is clearly deficient. Ours is a proposal to begin a multi-phase effort to realize technologies and interventional techniques that will make it possible to perform extraordinarily delicate and intricate cardiac procedures on a fetus while it is in the mother's womb, i.e., using minimally invasive in utero techniques. The overall concept is to provide the interventionalist graphical displays, navigation aids and in vivo sensing capabilities that enable a PCI and confirm its efficacy. The essence of our approach is to make minor augmentations of the equipment and devices currently used for PCI, but in so doing to make a significant increase in the information content provided to the interventionalist. The specific research proposed here is to develop an optical position tracking solution for instruments used in PCI that will enable their relative locations to be measured with high accuracy and in real time. Based on those data, a graphical display that combines ultrasound imagery and navigation data will readily created. With this real time display, the interventionalist will have the means to visualize the exact location of catheters and introducers even if they not clearly evident in the ultrasound images. Further, the display will show other salient geometric features, such as the trajectory a catheter will follow if it is inserted further and distances and angles between that tool path and the ultrasound image. The prototype system will be based on three technologies we have developed for orthopaedic surgery. This research will be conducted in partnership with Carnegie Mellon University's Robotics Institute and the Cardiology Department of Children's Hospital of Pittsburgh. In Phase Two, we will conduct in vivo tests of the sensors in appropriate animal models.